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Aquaculture 227 (2003) 173–189
Technical and economical feasibility of a rotifer
recirculation system
G. Suantikaa,*, P. Dhertb, E. Sweetmanc, E. O’Brienb, P. Sorgeloosa
aLaboratory of Aquaculture and Artemia Reference Center, Ghent University, Rozier 44, B-9000 Ghent, Belgiumb INVE NV, Oeverstraat 7, B-9200 Baasrode, Belgium
cEcomarine Ltd., Samoli, Livadi, 28200 Lixouri, Cephalonia, Greece
Accepted 29 May 2003
Abstract
A feasibility study was performed on the use of a recirculation system for the mass culturing of
rotifers at industrial level. Rotifer culture systems with a culture volume of 750 l were operated at
three different stocking densities (3000, 5000 and 7000 individuals ml� 1) in a completely closed
recirculation system. At all operating rotifer densities, a reliable production of 2.2 billion rotifers
could be obtained on a daily basis during 3 weeks. Excellent water quality was maintained by the use
of protein skimmers, the use of ozone and a submerged biofilter. The microbial counts remained
stable during the whole culture period (106 CFU ml� 1 on marine agar and 104 CFU ml� 1 on TCBS
after 15 and 23 days, respectively). No difference in HUFA and protein content were obtained
between rotifers harvested from the recirculation system or from a conventional batch culture system.
Compared to a commercial batch culture system, the use of a recirculation system can contribute to a
43% saving on the capital investment and the annual operation cost. By using this system, capital
investment cost is considerably reduced by 46%. Savings are also made on labour cost (65%) and
feed cost (21%) during a 1-year production.
In general terms, it can be stated that by using a simple recirculation system, a cost-effective
technology and a reliable rotifer culture can be obtained.
D 2003 Elsevier B.V. All rights reserved.
Keywords: Brachionus plicatilis; Recirculation; Rotifers; Ozone; Protein skimmer; Operational cost
0044-8486/$ - see front matter D 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0044-8486(03)00502-7
* Corresponding author. Laboratorium Ekologi, Departemen Biologi, Institut Teknologi Bandung, Labtek XI,
Jalan Ganesha 10, 40132 Bandung, Indonesia.
E-mail addresses: gsuantika@yahoo.com, gsuantika@bi.itb.ac.id (G. Suantika).
G. Suantika et al. / Aquaculture 227 (2003) 173–189174
1. Introduction
The economic profitability of larval rearing in marine finfish hatcheries depends
to a large extent on the continuous availability of high quality live food. In this
respect, the demand for rotifers has gradually increased over the last years which
can be explained by the relatively stagnating Artemia supply for an increased
aquaculture production. The most extreme need for rotifers can probably be found
in Japan where an average hatchery requires 20 billion rotifers day� 1 (Fushimi,
1989; Fu et al., 1997). The increasing need for rotifers forces hatcheries to re-
organize hatchery space and to employ extra personnel or intensify the mass pro-
duction of rotifers. As a result, these factors have a direct impact on the larval
production cost.
The cost of rotifer production depends to a large extent on the rearing technique
applied in hatcheries. In some European hatcheries, rotifers are cultured in batch
systems using algae and yeast as a food source. This type of rotifer production is
labour intensive and results in an average cost of o0.4 per million rotifers (Candreva et
al., 1996; Komis, 1992). In Japan, prefectural hatcheries are characterized by their large
size and a preference for more automated large-scale culture systems. Some prefectural
hatcheries have invested in the continuous culture of rotifers and the use of concentrated
algae (Fu et al., 1997; Yoshimura et al., 1997). In these sophisticated rearing systems,
the cost of rotifer production is estimated at o0.05 per million of which food accounts
for 86% (Fu et al., 1997). Labour cost in these hatcheries has been reduced to 13%
which is about half the cost of that which is generally accepted for European rotifer
production (28%).
In European hatcheries, the biggest problem in rotifer production systems is the
unpredictability of such systems (Candreva et al., 1996) which require several
duplicate and back up cultures. These extra production units have a direct impact
on the labour cost and the final competitiveness of the whole production. In order to
solve these problems, new rearing systems need to be developed primarily to increase
production stability and productivity and secondly to reduce the labour and investment
cost.
Based on this philosophy, an experimental rotifer recirculation system (Suantika
et al., 2000, 2001) was adapted for the needs of the industry. A pilot rotifer
production system was constructed and a financial study was performed to
evaluate the benefits of the system compared to the conventional rotifer batch
system.
2. Materials and methods
2.1. Rotifer strain
All experiments were performed with Brachionus (lorica length: 185F 15 Am)
originating from batch cultures reared following the culture procedure described in
Sorgeloos and Lavens (1996).
2.2. Experimental set up
The culture rearing tank (1 m3) was filled with diluted seawater (25 ppt salinity) and
maintained at a constant temperature of 25F 1 jC.Fig. 1 gives a schematic outline of the recirculation culture system used for the
high-density production of rotifers. The essential parts of the recirculation system
prototype are illustrated in Fig. 2. The tank was equipped with a central nylon screen
(mesh size of 33 Am) to retain the rotifers in the tank (Fig. 2B). Due to the dimension
of the central filter (0.5 m diameter, 0.9 m length), the available water volume to
culture rotifers (Fig. 2A) was reduced to 750 l. An aeration collar enclosed on the
outer bottom part of the filter created a constant aeration (2.1F 0.2 l min� 1) ensuring
a continuous cleaning of the filter and a homogenous distribution of food and rotifers.
A floccule trap (0.3 m diameter, 0.6 m length) based on an air–water-lift principle
was built in the culture tank to trap organic waste material from the tank (Fig. 3). The
flow rate over the air–water lift was 120 l h� 1. The effluent water from the culture
tank flowed by gravity to a 100-l settlement tank from where it was pumped to a
series of protein skimmers (Aqua Medic, Germany) (Fig. 2C). In the first protein
skimmer, ozone was injected at the flow rate of 500 mg l� 1 h� 1 to improve the
removal of suspended solids and soluble protein (Dhert et al., 2000; Suantika et al.,
2001). In order to improve the efficiency of the ozonisation, the incoming air was
dried through 1500 g silica gel that was renewed every 24 h. The ozone concentration
in the protein skimmer was controlled by measuring the redox potential (SMS510,
Milwaukee Instruments, USA). The ozone supply was automatically switched off
when a redox potential of 450 mV was exceeded. Residual O3 was stripped from the
effluent water by the action of the second and the third protein skimmer which also
removed residual particles and soluble proteins. The recirculation rate over the protein
skimmer was set at 1200 l h� 1 using a closed loop in the circuit. After the physical
separation in the protein skimmer, the effluent water was filtered over a submerged
biofilter (Fig. 2D) with a capacity of 750 l filled with 350 l (f 500 kg) gravel
(size = 3–8 mm) and 100 l (f 160 kg) CaCO3 (pH buffer, size = 10–20 mm). The
biofilter was inoculated with an enriched culture of nitrifying bacteria (105 CFU ml� 1,
ABIL Aqua, Belgium) 6 days before the inoculation of rotifers in the culture tank
(Suantika et al., 2001). After the biological filtration, the treated water was pumped
into the fourth protein skimmer in order to remove the bacterial flocs from the
biofilter. The O2 saturated water (7 mg l� 1) was then discharged into the culture tank
at a daily water renewal rate of 500% (f 200 l h� 1). The experimental set up was
used for three rotifer culture trials starting with an initial density of 500 individuals
ml� 1. In each of the culture trials, the rotifers were allowed to grow until they
reached 3000, 5000 and 7000 individuals ml� 1. As soon as these densities were
reached, the rotifer density was kept constant by daily harvest of the rotifers produced
in excess of the set density. During these harvests, new diluted seawater was added to
compensate for the loss in water volume (Table 4). Besides this, no other water
changes were performed during the culture period. Due to electrical problems during
the experiment, the trial with 5000 individuals ml� 1 stocking density was terminated
on day 21.
G. Suantika et al. / Aquaculture 227 (2003) 173–189 175
Fig. 1. Schematic overview of the recirculation system used for high-density rotifer production. PP: peristaltic pump, AW: air–water lift, F: nylon filter, SH: submerged
heater, P: pump.
G.Suantika
etal./Aquacultu
re227(2003)173–189
176
Fig. 2. Overview of main equipment used in the rotifer recirculation system prototype. (A) Rotifer culture tank
with the central filter. (B) Filter of 33 Am retaining the rotifers in the system. (C) Set of protein skimmers for
particle removal. (D) Submerged biofilter.
G. Suantika et al. / Aquaculture 227 (2003) 173–189 177
2.3. Rotifer diet
The rotifer diet consisted of an experimental Culture Selco, CSH (INVE, Belgium) (De
Wolf et al., 1998; Dhert et al., 1998, 2000; Suantika et al., 2000, 2001) suspended in 4.8-
l water and mixed vigorously with a kitchen blender. The suspension containing exactly
the daily food ratio was kept in suspension by aeration in a 10-l food container at ambient
temperature (20F 1 jC) for 24 h. Under ideal circumstances, cooling of the food should
be foreseen but this is often not available in commercial hatcheries. From the food
container, the food was administered automatically by means of a peristaltic pump to the
culture tank at 30-min interval (feeding 200 ml h� 1 or 4.8 l food suspension day� 1). The
rotifers were fed following a standard feeding regime (Suantika et al., 2000):
CSH ¼ 0:035D0:415V ;
where CSH= the weight of experimental diet (g), D = rotifer density (individuals ml� 1),
V= culture water volume (l).
Fig. 3. Schematic overview of the floccule trap used in the intensive rotifer culture tank.
G. Suantika et al. / Aquaculture 227 (2003) 173–189178
This feeding regime implies a high ration at start feeding to reach an acceptable diet
concentration for a small filtering rotifer population and it allows a faster bacterial
colonisation.
2.4. Sampling and counting
Rotifer counts were obtained from four subsamples of 400 Al taken from the rotifer
culture using an automatic micropipette. The rotifers in each sample were killed by
adding three drops of lugol. Empty and transparent loricae belonging to dead rotifers
were not counted. The specific growth rate was calculated using the following
equation:
l ¼ ðlnNt � lnN0Þ=t
G. Suantika et al. / Aquaculture 227 (2003) 173–189 179
where l = specific growth rate, Nt= rotifer density after culture period t (individuals
ml� 1), N0 = initial rotifer density (individuals ml� 1), t= culture period (day).
2.5. Length of rotifers
In order to document the effect of a long-term culture period on the size characteristics
of rotifers, regular samples were taken for lorica length measurement. Fifty rotifers were
placed on an objective glass and immobilized by low pressure of a cover glass without
addition of killing and staining agents to avoid shrinking of rotifers during measurement.
2.6. Physico-chemical parameters
The pH, NH4+, NO2
�, NO3� and the dissolved oxygen (DO) of the water were measured
as first daily activities during the experiment. NH4+, NO2
� and NO3� were performed on
filtered culture water (30 Am) of the rotifer tank using test kits (AquamerckR, ViscolorEcoR, Germany).
2.7. Bacterial sampling
Microbiological analyses were performed on a weekly basis by sampling 10 ml
from (1) the rotifer culture tank, (2) the outlet of the first protein skimmer and (3) the
outlet of the biofilter. Serial dilutions (10� 1, 10� 2, 10� 3, 10� 4) were prepared in
sterile saline solution (1.5%) from the homogenised water samples and 100 Al was
plated in duplicate on MA (marine agar) (Difco, USA) and TCBS (thiosulphate citrate
bile sulphate agar). The plates were incubated at 25 jC and bacterial counts performed
after 48 h.
2.8. Protein and fatty acid analysis
In order to investigate the oxidative effect of ozone on the nutritional content of the
rotifers, their protein and fatty acid content were analysed on days 1, 6, 11 and 16 of the
harvesting period from the tank containing 3000 individuals ml� 1 (trial I). Protein content
and fatty acids were measured by Kjeldahl and FAME analysis (Lepage and Roy, 1984),
respectively.
2.9. Economic and financial analysis
Capital and operational costs for the recirculation system were compared with those
from a commercial batch culture system with a production capacity of 2 billion rotifers
day� 1.
2.10. Statistical analysis
All data were statistically treated using one-way ANOVA. Significant differences
among means (P < 0.05) were tested by Duncan’s multiple range test.
G. Suantika et al. / Aquaculture 227 (2003) 173–189180
3. Results
3.1. Rotifer culture and production characteristics
The line diagrams in Fig. 4 illustrate the increase in rotifer density as a result of the
three different harvesting strategies. The daily harvest is illustrated in the block diagram.
Fig. 4. Rotifer density (solid line) and daily rotifer harvest (solid bar) obtained in recirculation systems kept at
3000 (a), 5000 (b) and 7000 individuals ml� 1 (c). Dotted lines show the reduction in rotifer density obtained by
daily harvesting.
G. Suantika et al. / Aquaculture 227 (2003) 173–189 181
During the first 4 days of the culture, no significant difference (P < 0.05) was noticed in
the specific growth rate of the rotifers of the different treatments. In the three treatments,
the specific growth rate of the rotifers was stable (0.50) and a rotifer density of 4000
individuals ml� 1 was reached after 4 days. Based on the specific growth rate of the
rotifers, it could be calculated that densities of, respectively, 3000, 5000 and 7000
individuals ml� 1 were reached after 3.8, 5.1 and 7.0 days. First daily harvests could thus
be performed on the respective tanks on days 5, 6 and 8 when rotifer densities reached,
respectively, 3700, 6000 and 7500 individuals ml� 1 (Fig. 4). In the first system where
after each daily harvest the rotifer density was reduced to 3000 individuals ml� 1 (Fig. 4a),
an average daily increase to 5750 rotifers ml� 1 was noticed corresponding to an average
specific growth rate of 0.61. During this period, a total of 51�109 rotifers were produced.
After 27 days, the cultures were stopped due to fouling and accumulation of dirty particles
in the culture tank. In the second system (5000 individuals ml� 1), an average increase to
6700 rotifers ml� 1 was noticed (Fig. 4b) corresponding to an average specific growth rate
of 0.40. During this period, a total of 33� 109 rotifers were produced. In the third system
(7000 individuals ml� 1), an average increase to 9500 rotifers ml� 1 was noticed (Fig. 4c)
corresponding to an average specific growth rate of 0.26. During this period, a total of
34� 109 rotifers were produced.
In the rotifer-rearing experiment, where the rotifers were kept at a density of 3000
individuals ml� 1, length measurements were performed on a daily basis. The average
length of the rotifers obtained during the experiment is shown in Fig. 5. At the start of the
experiment, the lorica length of the rotifers, including neonates and adults, was 191F 7 Am,
it increased significantly during the second week of culture (211F 9 Am) after which it
decreased to the original size in the third week to measure (182F 4 Am) in the fourth week.
3.2. Physico-chemical parameters
Table 1 shows the range in physico-chemical parameters recorded in the recirculation
system for the three different operational rotifer densities. For all treatments, the pH level
Fig. 5. Changes in rotifer length during the culture experiment at 3000 rotifers ml� 1. Data points are average
values of daily measurements. Averages with a same letter are not significantly different ( P >0.05).
Table 1
The physico-chemical parameters measured in the recirculation system
3000 individuals ml� 1 5000 individuals ml� 1 7000 individuals ml� 1
Before
harvesting
During
harvesting
Before
harvesting
During
harvesting
Before
harvesting
During
harvesting
day 1 day 5 day 6 day 27 day 1 day 6 day 7 day 21 day 1 day 8 day 9 day 27
pH 7.6 7.3 7.3 7.4 7.8 7.5 7.4 7.5 7.9 7.5 7.5 7.2
NH4+
(mg l� 1)
0.4 0.5 0.6 0.8 0.2 0.4 0.6 0.8 0.2 0.4 0.6 1.0
NO2�
(mg l� 1)
0.7 2.5 3.0 1.3 0.5 1.3 1.5 3.0 0.5 2.5 3.8 0.4
NO3�
(mg l� 1)
10 70 80 25 15 25 30 150 10 25 100 13
DO
(mg l� 1)
6.7 4.4 4.4 3.6 nd nd nd nd 6.5 3.4 2.2 1.2
nd = no data.
G. Suantika et al. / Aquaculture 227 (2003) 173–189182
decreased slightly before harvesting. A stable pH level was obtained as soon as the daily
harvests were performed for the treatments at 3000 and 5000 individuals ml� 1. For the
treatment where the rotifers were harvested at 7000 individuals ml� 1, a slow decrease in
pH was noticed.
Low and slowly increasing ammonium levels were observed during the culture period
at the three different stocking densities.
Low nitrite levels (NO2�) were also obtained in the system during the culture period. In
general, the NO2� level increased before the harvesting period and decreased during the
periodical harvesting. The NO2� levels increased from 0.7 to 2.5 and 0.5 to 2.5 mg l� 1
before harvesting and decreased from 3.0 to 1.3 and 3.8 to 0.4 mg l� 1 during the
periodical harvesting ( = addition of fresh seawater) at 3000 and 7000 individuals ml� 1
stocking density, respectively. For the system where rotifers were kept at 5000 individuals
ml� 1, an opposite trend was noticed. The NO2� level increased continuously from 0.5 to
3.0 mg l� 1 which was most probably the result of a failure in O2 supply (electricity failure
on days 15 and 19).
Increase of nitrate (NO3�) levels were observed in the beginning of the culture period
(before harvesting) and decreased slightly during the daily harvests. The NO3� levels
decreased from 80 to 25 and 100 to 13 mg l� 1 during the periodical harvesting at 3000
and 7000 individuals ml� 1 stocking density. However, the NO3� level increased drastically
from 30 to 150 mg l� 1 at 5000 individuals ml� 1 stocking density which is again a result
of the electricity failure.
Dissolved oxygen decreased relatively fast during the period before harvesting for 3000
and 7000. It could be maintained around 4 mg l� 1 by the water supplementation in 3000
individuals ml� 1 while in 7000 individuals ml� 1 it was reduced to 1 mg l� 1.
3.3. Bacterial counts
The bacterial counts performed on water sampled from the rotifer culture tank, the
protein skimmer and the biofilter is given in Table 2. After 7 days of culture, the amount of
Table 2
Bacterial counts obtained from water sampled in the rotifer culture tank (5000 individuals ml� 1), after the protein
skimmer and after the biofilter
Sample Marine Agar
(CFU ml� 1)
TCBS
(CFU ml� 1)
Recirculation
Day 7 rotifer culture tank 3.4� 106 1.6� 105
after protein skimmer 1.8� 105 2.2� 104
after biofilter 1.4� 106 3.5� 103
Day 15 rotifer culture tank 3.4� 106 3.8� 104
after protein skimmer 4.1�106 3.5� 103
after biofilter 4.9� 105 0
Day 23 rotifer culture tank 2.3� 105 3.0� 104
after protein skimmer 2.8� 104 5.5� 103
after biofilter 3.5� 104 0
Batch rotifer culture tank 3.7� 107 nd
nd: no data.
G. Suantika et al. / Aquaculture 227 (2003) 173–189 183
bacteria in the rotifer culture water was 3.4� 106 and 1.6� 105 CFU ml� 1 on marine agar
and on TCBS, respectively. In the following weeks, no significant difference in bacterial
numbers were noticed. Bacterial numbers recorded after the protein skimmer tended to be
1 log unit lower than in the culture water for marine agar and TCBS counts. Vibrio counts
were low (3.5� 103 CFU ml� 1) for samples taken after the biofilter at the end of the first
week of culture. No vibrios were noticed from the second week onwards.
3.4. Nutritional content of the harvested rotifers
The HUFA and protein content of the harvested rotifers are given in Table 3. The
HUFA levels ranged from 10.0 to 11.4 mg.g� 1 DW during the culture period and the
DHA/EPA ratio ranged from 0.52 to 0.66. During the whole culture period, the protein
content was higher than 50%.
3.5. Economic and financial analysis
Table 5 gives an idea of the total capital investment required to run a commercial
batch system and to run a recirculation system with a daily production output of 2
Table 3
Nutritional content of harvested rotifers cultured in the recirculation system (3000 individuals ml� 1)
Day Protein
(% DW)
DHA
(mg g� 1 DW)
EPA
(mg g� 1 DW)
DHA/EPA S(n� 3) HUFA
(mg g� 1 DW)
Recirculation
1st day harvest 55.6 2.5 4.8 0.52 10.1
6th day harvest 52.3 3.0 4.8 0.63 10.3
11th day harvest 56.8 3.5 5.4 0.64 10.4
16th day harvest 51.2 3.1 4.7 0.66 10.0
Batch – 3.5 4.9 0.70 11.8
G. Suantika et al. / Aquaculture 227 (2003) 173–189184
billion rotifers. For the batch system, the total capital cost is about o52,139, the
majority of the cost (77%) is spent for investment on fixed assets while general and
scientific equipment accounts for 23%. For a recirculation system, a lower capital
investment of o28,000 is required. In the recirculation system, most of the cost (70%)
is spent for investment on fixed assets and 30% is consumed by general and scientific
equipment. Using the batch system, the total annual running cost to produce 2 billion
rotifers day� 1 is around o42,200 made up for 34% in feed cost, 33% labour cost and
25% for depreciation of fixed assets. Total annual running costs for the recirculation
system is also lower than for the batch culture system since o25,800 is needed to
produce 2 billion rotifers day� 1; i.e. 43% feed cost, 19% labour cost and 28% for
depreciation of fixed assets (Table 6).
4. Discussion
A lot of disadvantages inherent to a conventional batch culture system can be solved by
the use of a recirculation system, as the latter allows to increase rotifer production, reduce
labour cost and water consumption while ensuring stable water quality (Suantika et al.,
2000). In the batch culture, maximum rotifer densities of 3000 individuals ml� 1 were
reached after 4 days of culture period (De Wolf et al., 1998). After this, the rotifers need to
be rinsed and returned to the system which is a labour intensive process. On the other
hand, in the recirculation system a production of nearly 3000 individuals ml� 1 can also be
obtained after a culture period of 4 days but the rotifer culture can be maintained for
almost 1 month without rinsing and restocking the rotifers (Fig. 4). During this whole
culture period, it was possible to produce 2.2 billion rotifers day� 1.
Our experiments (Table 4) show that operating the system at the lowest density (3000
individuals ml� 1) resulted in 29% faster growth rate of the rotifers compared to the
system operated at the highest density (7000 individuals ml� 1). Although the use of a
lower operational rotifer density results in an increase in production, it has also some
operational disadvantages. Due to the lower density, up to 45% of the standing crop
needs to be harvested daily which in a commercial operation may cause problems when
the rotifer requirement is not constant. The higher water renewal of 45% at low standing
crop is advantageous for water quality and results in better NO3� removal and an
Table 4
Rotifer production during a 30-day culture period in a 1-m3 recirculation system
Stocking density (mg l� 1)
3000 5000 7000
Average daily production (rotifers day� 1) 2.2� 109 2.1�109 1.7� 109
Water renewal (l day� 1) 382 (45%) 314 (37%) 178 (21%)
Specific growth rate 0.61 0.40 0.26
S water consumption (l) 9600 7840 4500
S food (kg) 21 25 28
(%): percentage of standing population.
G. Suantika et al. / Aquaculture 227 (2003) 173–189 185
increased dissolved oxygen level (Table 1). On the other hand, this higher water renewal
increases the risk for upwelling of sedimentation and destabilisation of the system.
Probably the most important advantage of operating at the lowest standing crop resides
in the 25% saving on food consumption which could significantly reduce the rotifer
production cost which is estimated at 60% of the total production cost in batch systems
(Lavens et al., 1994).
By operating the system at the lowest standing crop, acceptable dissolved oxygen levels
could be maintained. The DO levels only decreased 2.9 mg l� 1 (from 6.5 to 4.4 mg l� 1)
during the whole culture period; a similar or even higher decrease was already measured
after 4 days in the batch culture (Suantika et al., 2000). In a continuous culture system, Fu
et al. (1997) noticed that stable daily rotifer production can be achieved by stabilising the
oxygen levels at around 4.5 mg l� 1. In this regard, further optimisation of the system
could be envisaged by the use of pure O2 in the culture tank especially when higher
operational rotifer densities need to be maintained.
Acceptable values were measured for all water parameters in the recirculation system at
the three different operating densities. For example, pH levels decreased less than 0.5 units
during the whole culture period, whereas these changes are already measured in a batch
system after 4 days (Suantika et al., 2000). Also low accumulation of ammonium, nitrite
and nitrate were obtained in the recirculation system. It can be explained that the daily
addition of new seawater to compensate for the losses of culture water contributed to a
better control for the physico-chemical parameters and also indirectly reduced the load of
the biofilter. Beside daily water renewal, the supplementation of ozone in the recirculation
system also contributed to stable and low accumulation of ammonium, nitrite and nitrate
(Suantika et al., 2001). Although an opposite trend was noticed for the system ran at 5000
individuals ml� 1, it is very likely that this was due to the effect of a total electricity failure
and not linked to any density problem at all. It is obvious that the improved water quality
had a positive effect on the growth of the rotifer population. Apparently, the better rearing
conditions also had an effect on the rotifer lorica size. During the first week, the average
lorica size increased and rotifers originating from a batch culture showed an increase of
F 10% in length. This is in accordance with the observation of Lubzens (1987) who stated
that changes in lorica length of up to 15% can be noticed due to changing water quality.
The size of rotifers significantly decreased starting day 21 (last week of culture period)
when the culture condition started to deteriorate. Starting from this period, fouling of the
tank created more dirt particles in the culture water resulting in a less stable bacterial
community (Rombaut et al., 2001).
The use of a recirculation system for daily rotifer production obviously also has
advantages on the bacterial numbers in the system. Bacterial numbers obtained in rotifers
tend to be 1 to 2 log units lower than in a batch system (Rombaut et al., 2001). Moreover,
the shift in bacterial communities (elimination of vibrios in the biofilter) could be
beneficial when rotifers are used as larval food. From this result, it can be anticipated
that a better conditioning of the nitrifying bacteria in the biofilter might also pay off before
starting a new culture. Better control of the vibrio community in the rearing system is
presently under investigation and could possibly be obtained by a combination of higher
filtration rates and active bacterial management (i.e. combination of inoculation and
disinfection techniques).
Table 5
Estimated capital investment for a batch system and a recirculation system with a production capacity of 2 billion
rotifers day� 1
Facility Item Batch system Recirculation system
Quantity Total cost
(Euro)
Quantity Total cost
(Euro)
(A) Buildings Concrete base (inc. channels) 30 m2 3510 20 m2 2340
Building/partitioning 160 m2 2400 100 m2 1500
Rotifer room floor 310 m2 3100 200 m2 2000
Service gantry 30 m 11,160
(B) Other installations Fresh water 1 73 1 73
Pipework installations water 1 729 1 729
Pipework installations air/O2 1 729 1 729
Electrical installations 1 2625 1 2625
(C) Plant and machinery Live food filter 1 1167
Live food blower 1 1896
Rotifer culture heating unit 1 2100
Air filter 1 1021
Peristaltic pump 1 744
Protein skimmer 4 1280
Eheim pump 12 888
Blower 1 1487
O3 generator 6 1338
ORP meter 2 248
(D) Tanks General purpose tanks 6 1752
Rotifer tanks 11 8019
1000-l tanks with frame 1 250
100-l settlement tanks 1 32
(E) General and Microscope 1 set 3584 1 set 3584
scientific equipment Haemocytometer 1 66 1 66
Portable pH meter 1 395 1 395
Portable O2 meter 1 467 1 467
Netting 20 1440 20 1440
Refrigerator 1 372 1 372
Airline 1 set 248 1 set 248
Laboratory balance 1 350 1 350
Blender 1 321 1 321
Tank heaters 11 2563 6 2563
Small lab. equipment 1 set 1095 1 set 1095
Oxygen stones 11 957
(F) Filtration 1000-l biofilter tank 1 372
Stone (substrate biofilter) 3000 kg 87
Air filter 1 5
Filter frame 1 87
Nylon filter mesh 1700 m2 63
PVC air–water lift 1 62
Filter sponge 2 m2 21
(G) Tubing PVC tubing 2 248
Flexible PVC tube 40 m 35
Total capital cost 52,139 28,144
G. Suantika et al. / Aquaculture 227 (2003) 173–189186
G. Suantika et al. / Aquaculture 227 (2003) 173–189 187
The nutritional content of harvested rotifers from the recirculation system did not
differ from this obtained from rotifers originating from batch cultures. The harvested
rotifers contained a normal fatty acids and protein content (Table 3), and could,
depending on the fish species to be cultured, used as such or further enriched (Dhert
et al., 2001).
From an economical point of view, the use of a recirculation system also has a lot of
advantages. Investment, labour and feed costs are considerably reduced compared to the
conventional batch culture system (Tables 5 and 6). For example, to produce 2 billion
rotifers day� 1, the investment cost is 46% lower. Savings are mainly made on
equipment (especially rotifer tanks and heating systems). Also, the annual operation
cost is lower due to savings on labour. One person working 2 h/day (e.g. counting rotifer
density, measuring water quality, rotifers harvesting, filter rinsing and feeding) can easily
handle two rotifer recirculation systems. Compared to the batch system the gain in
managing the system is estimated at o14,000. The better food conversion rate obtained
Table 6
Estimated annual operation cost to produce 2 billion rotifers day� 1 in batch system and recirculation system
(5000 individuals ml� 1 stocking density)
Item Description Batch system Recirculation system
Quantity Total cost
(Euro)
Quantity Total cost
(Euro)
(A) Labour Hours per year 14� 143 h
(2000 h/year)
14,000 14� 50 h
(700 h/year)
4900
(B) Electricity Tank heating,
direct heating/cooling,
air supply/blower, etc.
60 kW� 12 14 30 kW� 12 7.2
Pumps, automatic
feeding machine
20 kW� 12 4.8
(C) Consumables Tank heaters replacements 3 699 3 33
Cleaning materials 12 583 1 24
Netting for
rinsers/concentrators
3 583 3 189
Miscellaneous material,
pipelines, O2 stones, etc.
5 365 5 365
Lights—replace once per year 8 16 8 16
Water quality test kits 6 534
(D) Feed Culture Selco 360 kg 11,156
Protein Selco 5 kg 300
DHA Protein Selco 5 kg 325
CSH 300 kg 11,154
Algae 137 m3 2329
(E) Miscellaneous Various 1458 1458
Total running costs 38,813 26,626
(F) Depreciation Depreciation on capital
costs 20% per annum
20% 10,428 20% 7173
Total running cost
including capital
depreciation
42,257 25,858
Fig. 6. Estimated capital cost (Euros) and operational cost (%) to produce 2 billion rotifers day� 1 in a batch
system and a recirculation system.
G. Suantika et al. / Aquaculture 227 (2003) 173–189188
in the recirculation system (Suantika et al., 2000), can also account for 10% savings. In
general, the use of the recirculation system can reduce the investment and operational
costs for about 43% (Fig. 6). In percentage, there are no differences obtained on
investment cost, depreciation cost and other costs between the commercial batch culture
system and the recirculation system. By using a recirculation system, saving is mainly
made by a reduction of the labour cost from 15% to 9%. When expressed in percentages
the cost for feeds is increased using a recirculation system, however, on an absolute
basis the cost for feeds remains identical with the batch system. It can be explained that
to support optimum growth rate of rotifers in the recirculation system, a 20% higher
amount of food is needed to compensate for food losses through the system, but since
more efficient food uptake is obtained by denser rotifer cultures this results in a similar
food consumption. In conclusion, it can be stated that by using a simple recirculation
technology, a cost-effective and above all reliable rotifer culture can be obtained.
Moreover, the system opens new perspectives in terms of automated production of
clean and healthy rotifers.
Acknowledgements
This study was supported by the Indonesian Government and managed by the center
grant of the Department Biology-Institut Teknologi Bandung, under contract no. 010/CG/
III/URGE/1997, IBRD Loan no. 3754-IND. Part of this study was also supported by the
FWO project G. 006396 N.; CRAFT project Q5CR-2000-70186, DWTC and INVE,
Belgium. The Laboratory of Microbial Ecology and Technology, Ghent University
supplied the nitrifying bacteria. The authors wish to thank T. Baelemans for his technical
assistance during the experiment.
G. Suantika et al. / Aquaculture 227 (2003) 173–189 189
References
Candreva, P., Dhert, P., Novelli, A., Brissi, D., 1996. Potential gains through alimentation nutrition improvements
in the hatchery. In: Chatain, B., Sargalia, M., Sweetman, J., Lavens, P. (Eds.), Seabass and Seabream Culture:
Problems and Prospects. An International Workshop, 16–18 October 1996, Verona, Italy. Eur. Aquac. Soc.,
vol. 388, pp. 148–149.
De Wolf, T., Candreva, P., Dehasque, M., Coutteau, P., 1998. Intensification of rotifer batch culture using
artificial diet. In: Grizel, H., Kestemont, P. (Eds.), Aquaculture and Water: Fish Culture, Shellfish Culture
and Water Usage. Aquaculture Europe’98, Bordeaux, France, October 7–10, 1998. Spec. Publ.-Eur. Aquac.
Soc., vol. 2, pp. 68–69.
Dhert, P., Suantika, G., Nurhudah, M., Sorgeloos, P., 1998. High density production of rotifer (Brachionus
plicatilis) by improved culture and water quality management. In: Grizel, H., Kestemont, P. (Eds.), Aqua-
culture and Water: Fish Culture, Shellfish Culture and Water Usage. Aquaculture Europe’98, Bordeaux,
France, October 7–10, 1998. Spec. Publ.-Eur. Aquac. Soc., vol. 2, pp. 68–69.
Dhert, P., Suantika, G., De Wolf, T., Okechi, J.K., Bonaldo, A., Sorgeloos, P., 2000. The use of ozone in a high
density rotifer recirculation system. In: Flos, R., Creswell, L. (Eds.), Responsible Aquaculture in the New
Millennium. AQUA 2000, Nice, France, May 2–6, 2000. Spec. Publ.-Eur. Aquac. Soc., vol. 28, p. 182.
Dhert, P., Rombaut, G., Suantika, G., Sorgeloos, P., 2001. Advancement of rotifer culture and manipulation
techniques in Europe. Aquaculture 200, 129–146.
Fu, Y., Hada, H., Yamashita, T., Yoshida, Y., Hino, A., 1997. Development of continuous culture system for
stable mass production of the marine rotifer Brachionus. Hydrobiologia 358, 145–151.
Fushimi, T., 1989. Systemizing large scale culture methods. In: Fukusho, K., Hirayama, K. (Eds.), The First Live
Feed Brachionus plicatilis. Koseisha Koseikaku, Tokyo, pp. 118–134.
Komis, A., 1992. Improved production and utilization of the rotifer Brachionus plicatilis Muller. European Sea
Bream (Sparus aurata Linnaeus) and Sea Bass (Dicentrarchus labrax Linnaeus) larviculture. Laboratory of
Aquaculture and Artemia Reference Center, Ghent University, Belgium, pp. 155–189.
Lavens, P., Dhert, P., Merchie, G., Stael, M., Sorgeloos, P., 1994. A standard procedure for the mass pro-
duction on an artificial diet of rotifers with a high nutritional quality for marine fish larvae. In: Chou, L.M.,
Munro, A.D., Lam, T.J., Chen, T.W., Cheong, L.K.K., Ding, J.K., Hooi, K.K., Khoo, H.W., Phang, V.P.E.,
Shim, K.F., Tan, C.H. (Eds.), The Third Asian Fisheries Forum, Manila, Philippines. Asian Fishery Society,
Japan, pp. 745–748.
Lepage, G., Roy, C.C., 1984. Improved recovery of fatty acid through direct transesterification without prior
extraction or purification. J. Lipid Res. 25, 1391–1396.
Lubzens, E., 1987. Raising rotifers for use in aquaculture. Hydrobiologia 147, 245–255.
Rombaut, G., Suantika, G., Boon, N., Maertens, S., Dhert, P., Sorgeloos, P., Verstraete, W., 2001. Monitoring of
the evoluting diversity of the microbial community present in rotifer cultures. Aquaculture 198, 237–252.
Sorgeloos, P., Lavens, P., 1996. Manual on the production and used of live food for aquaculture. Fisheries
Technical Paper, vol. 361. Food and Agriculture Organization of the United Nations, Rome, pp. 49–78.
Suantika, G., Dhert, P., Nurhudah, M., Sorgeloos, P., 2000. High-density production of the rotifer Brachionus
plicatilis in a recirculation system: consideration of water quality, zootechnical and nutritional aspects. Aquac.
Eng. 21, 201–214.
Suantika, G., Dhert, P., Rombaut, G., Vandenberghe, J., De Wolf, T., Sorgeloos, P., 2001. The use of ozone in a
high density recirculation system for rotifers. Aquaculture 201, 35–49.
Yoshimura, K., Usuki, K., Yoshimatsu, T., Kitajima, C., Hagiwara, A., 1997. Recent development of a high
density mass culture system for the rotifer Brachionus rotundiformis Tschugunoff. Hydrobiologia 358,
139–144.
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